KR940000732B1 - Method and apparatus for producing a liquefied permanent gas stream - Google Patents

Abstract

A stream of permanent gas such as nitrogen at elevated pressure is cooled to below its critical temperature by heat exchange with work-expanded working fluid. The stream 2 is then further cooled in heat exchanger 4 and successfully flashed through at least three expansion valves 6, 12 and 16. Resulting flash gas is separated from liquid gas in separators 10, 14 and 18 respectively. The flash gas is passed through the heat exchanger 4 to provide cooling for such heat exchanger. By performing at three such successive isenthalpic expansions instead of the conventional one or two expansions, greater thermodynamic efficiency can be achieved enabling more favourable conditions to be set for the work expansion of the working fluid.

Description

Permanent Gas Stream Liquefaction Method

1 is a process diagram illustrating a part of the nitrogen liquefaction plant according to the present invention.

Figure 2 is a graph of nitrogen versus enthalpy.

3 is a process diagram illustrating a nitrogen liquefaction plant according to the present invention.

4 is a diagram showing the relationship between plant equipment and temperature presented in FIG.

5 is a diagram showing the relationship between another nitrogen liquefaction plant equipment and temperature.

6 is a graph showing the specific heat-temperature curve of nitrogen under each pressure.

The present invention relates to refrigeration methods and apparatus and in particular to the liquefaction of permanent gases such as nitrogen and methane.

Permanent gas has a property of not being liquefied by only raising the pressure of the gas. In order to reach a temperature at which a gas can exist in equilibrium with its liquid, the gas needs to be cooled under pressure.

Conventional processes of liquefying permanent gas or cooling it to or below a critical point must compress the gas (usually unless it is properly elevated to above 30 atmospheres) and heat exchange with a relatively low pressure working fluid. Supply working fluid below the critical temperature of permanent gas. A stream of working fluid is typically formed by compressing the working fluid, cooling it in a heat exchanger and expanding it with the performance of external work (“thermal expansion”). The working fluid may be taken from the high pressure stream of the permanent gas and the permanent gas may be kept separate from the working fluid, nevertheless the working fluid may have the same components as the permanent gas.

Typically, liquefied permanent gas is stored and used at a pressure lower than its pressure for isothermal cooling below its critical temperature. Therefore, after completion of this isothermal cooling, the permanent gas below the critical temperature passes through an expansion or throttling value to sufficiently reduce the pressure and produce a large amount of so-called "flash gas". This expansion is an enthalpy process and results in a drop in the temperature of the liquid. Generally, one or two such expansion processes should be performed to produce liquefied permanent and ignition gases in equilibrium with steam at storage pressure. In general, there is no room to improve this efficiency because of the low thermodynamic efficiency of industrial processes for liquefying permanent gases.

The emphasis was on improving the overall efficiency of the process by increasing the efficiency of the heat exchanger. As such, the prior art in the art has focused on reducing the temperature difference between the permanent gas stream and the working fluid stream or the stream being heat exchanged.

I invented a method to improve the efficiency of the copper enthalpy expansion stage of the liquefaction process. This increase in efficiency is not a simple value previously possible, which allows more favorable conditions (or very low temperature thermal expansion) to be applied to the thermal expansion of the working fluid and thus can only be achieved by dynamic enthalpy expansion during liquefaction. It is possible to obtain greater overall thermodynamic efficiency improvements than there is.

The present invention provides a method of liquefying a permanent gas stream, which is described in the following four ways. first; Lowering the boosted permanent gas stream below its critical temperature. The temperature increase at this time is influenced by the counter flow heat exchange with the thermally expanded working fluid containing nitrogen. The temperature of this working fluid is also below the integral temperature of the permanent singer when it is heat exchanged with the permanent gas stream. second; Permanent gas streams below the critical temperature described above are subjected to at least three continuous dynamic enthalpy expansions. third; The flash gas generated in the liquid after copper enthalpy expansion is separated, and the liquid remaining in each copper enthalpy expansion process remains to the end as the fluid expanded in subsequent copper enthalpy expansion. fourth; The permanent gas stream exchanges heat with a portion of the ignition gas.

The present invention also provides an apparatus for liquefying permanent gas, including three things. first; And a heat exchanger. The apparatus has a passage of a boosted permanent gas stream in which heat exchange is to be made to the passage of the thermally expanded working fluid and also to the passage of the ignition gas. second; One or more thermal expansion devices. The apparatus causes the thermally expanded working fluid to be at or below the critical temperature of the permanent gas stream and thus to cool the temperature of the permanent gas stream below its critical temperature. third; The permanent gas stream includes three or more expansion valves for carrying out three or more accelerated dynamic enthalpy expansions. The downstream end of each valve is connected to a separator separating liquefied gas and ignition gas, and each separator containing liquefied gas has an outlet connected to the bottom of the next expansion valve.

Performing three or more continuous enthalpy expansions (copper enthalpy pressure reduction) between the initial temperature and the final temperature is thermodynamically more efficient than performing the same temperature range with only one or two dynamic enthalpy expansions. The reason why such greater efficiency can be obtained is set by the method of the embodiment with reference to FIG. 2 below.

Typically, after heat exchange with the permanent gas stream, the ignition gas is recompressed with the incoming permanent gas for liquefaction.

Typically, a thermally expandable working fluid is produced, and the working fluid is also compressed, cooled (by permanent gas), thermally expanded in an expansion turbine, warmed by countercurrent heat exchange to the permanent gas stream, where the permanent gas stream is Cooled), and countercurrent heat exchange takes place in the working fluid cycle which is returned for recompression.

If desired, two or more thermal expansion processes may be used in one working fluid cycle. As such, the working fluid in the middle of the cooling and heating process undergoes thermal expansion at intermediate pressures, some of which are reheated and thermally expanded to lower pressures, but usually at the same temperature obtained by the first stage of thermal expansion.

We use at least two working fluid cycles, where one working fluid is subjected to countercurrent heat exchange with permanent gas at low temperatures and proceeds at a temperature lower than the temperature of the other cycle.

In this method, it is believed that three or more dynamic enthalpy expansions can be used which result in a greater drop in working fluid temperature than conventional liquefaction methods. As such, the amount of refrigeration required for the lowest temperature working fluid cycle can be reduced, thus allowing relatively high expansion turbine outlet flow rates and outlet pressures to be used for this cycle. In a minimum temperature working fluid cycle, when the working fluid is at least 10 atm and one thermal expansion is completed, it is usually in the range of 12 to 20 atm (for example, the expansion turbine has a minimum of 10 atm, usually at a pressure of 12 to 20 atm). Most preferred. This outlet pressure is much higher than that conventionally used in turbine expansion cycles. Using this high pressure, the specific heat of the thermally expanded working fluid is actually high, which allows for the increase of the thermodynamic efficiency of the lowest temperature working fluid cycle and also reduces the specific power consumption. Preferably, when the thermal expansion is completed, the outlet pressure of the expansion turbine is 12 to 20 atm, and the working fluid is at a saturation temperature or 2 ° K higher than the saturation temperature. At or near saturation temperature, the specific heat of the working fluid increases rapidly with temperature drop.

Therefore, when the working fluid is thermally expanded to (or near) the saturation temperature, the advantage of increasing the thermodynamic efficiency by using the outlet pressure of the expansion turbine at least 10 atm. Indeed, once thermal expansion is complete, the autofluid is advantageously fully saturated or set. If two or more expansion turbines are used in the working fluid cycle, the turbine with the lowest pressure has an outlet temperature of 2 ° K higher than or equal to the saturation temperature of the working fluid.

It is desirable to heat exchange the permanent gas stream at a lower temperature with some or all of the ignition gases than when the thermally expanded working fluid is heat exchanged with the permanent gas stream. In a typical embodiment of this, the ignition gas is convinced that the temperature of the permanent gas stream can be reduced by 3 ° K and the advantage is that the temperature of the permanent gas stream to be heat exchanged with the ignition gas is required in the conventional process. This means that 3 ° K can be higher than the temperature. Therefore, it is possible to increase the outlet pressure of the expansion turbine to 10 atm or higher in the working fluid cycle at the lowest temperature.

It is desirable in the art to take advantage of the increase in efficiency by taking permanent gas streams which enthalpy expand at temperatures above conventional practice temperatures. According to the present invention, when the permanent gas is nitrogen, the temperature of the nitrogen is lowered to 107 to 117 ° K (usually 110 ° K) before injecting it into the continuous copper enthalpy expansion process described above. A temperature of 110 ° K can be used over the pressure of a wide range of permanent gas streams.

If the permanent gas is a nitrogen stream produced in a low temperature air separation process that produces hundreds of tonnes of oxygen per day, the ignition gas is typically produced at half the amount of liquid nitrogen produced, and the nitrogen stream produces a dynamic enthalpy expansion at 110 ° K. To use. In small plants where centrifugal compressors are used, when the outlet temperature of the expansion turbine is close to the working temperature of the working fluid, the rate of ignition gas is high (eg up to 100% of the rate of liquid product formation), resulting in increased circulation gas volume and circulation. The compressor efficiency is preferably maintained. If the turbine outlet temperature is close to the critical temperature, unless the exceptionally high outlet pressure is used (e.g., at least 20 atm when using nitrogen as the working fluid), it is not possible to maintain the outlet temperature of the expansion turbine within 2 ° K of the saturation temperature. impossible.

Typically, the permanent gas stream is also cooled by heat exchange with the freezer stream. The refrigerant stream is heat exchanged countercurrently with the permanent gas stream at or above the temperature at which the thermally expanded working fluid merges with the permanent gas stream. In the liquefaction of nitrogen, it is desirable to cool the permanent gas stream of the refrigerant stream to 210 ° K at room temperature. This is advantageous because in the high temperature thermal expansion step the refrigeration load can be reduced and operated more efficiently than other possible methods. Refrigerants are typically non-permanent gases used for "freon" or other refrigeration. The working fluid is typically permanent gas and is usually taken from the gas to be liquefied and compressed for convenience.

In general, it is desirable to maintain a very similar temperature-enthalpy profile of the permanent gas and the working fluid, in particular the maximum rate of change in the specific heat of the permanent gas (e.g. 135 ° K for nitrogen at 50 atmospheres). And more than 180 ° K).

The exact temperature and number of working fluid cycles at which the thermally expanded working fluid is heat exchanged back to the permanent gas are chosen to achieve this similarity.

It is preferable to use three working fluid cycles to achieve this job in the liquefaction of permanent gas provided at 45 atm or lower. By adopting three cycles, the refrigeration load at the lowest temperature cycle can be maintained at a level comparable to the operation of the expansion turbine in cycles with an outlet pressure of at least 12 atmospheres. In the embodiment of nitrogen liquefaction at 45 atm, the minimum temperature or outlet pressure at 16 atm is determined by the term "low temperature" (where "low temperature") employs an expansion turbine of FIG. Working fluid cycle, an intermediate stage working fluid cycle utilizing two expansion turbines having an outlet temperature of 136 ° K, also referred to as "high temperature" (herein referred to as "high temperature") using an expansion turbine with an outlet temperature of 160 ° K. Refers to the state of the working fluid with elevated temperature under compression). ”The working fluid cycle is employed. The higher the pressure of the permanent gas, the less complete the temperature enthalpy profile. Therefore, the close similarity between the temperature-endorpy profile of the permanent gas and the working fluid is easily maintained. Therefore, at permanent gas pressures above 45 atm, it is desirable to employ only two working fluid cycles. For example, a "low temperature" working fluid cycle using an outlet turbine with an outlet pressure of 14 atm and an outlet temperature of 110 to 112 ° K for 50 atmospheres of nitrogen and a "high temperature" working fluid cycle using an expansion turbine with an outlet temperature of 150 ° K is adopted. It is preferable to.

The permanent gas is preferably boosted by a suitable compressor, except where it can be supplied in a properly boosted condition. In one example, the pressure of the permanent gas is boosted to a final pressure through several stages of the multistage compressor and then to a final pressure by a rotary boost compressor connected together to the rotary shaft of the expansion turbine used for thermal expansion of the working fluid. Typically, different pressure streams of ignition gas are returned to each stage of the multistage compressor.

In order to reduce the number of passages connected to the heat exchanger device, it is desirable to share the passage of the working fluid cycle with the passages returned to the compressor via the heat exchanger.

The present invention is not limited to the liquefaction of nitrogen and methane. Other gases such as carbon monoxide and oxygen can also be liquefied.

The present invention will be described in more detail with reference to the drawings.

In FIG. 1, the liquid nitrogen stream 2 at a temperature of 113 ° K and a pressure of 45 atm drops through the heat exchanger 4 to 110 ° K. It is then depressurized to 8 atmospheres through a copper enthalpy throttling valve (6). At this pressure, a large amount of gaseous nitrogen flashes in the liquid passing through the valve 6 and the liquid nitrogen is maintained at 8 atmospheres. The ignition gas is separated from the liquid nitrogen in the phase separation tank 10. The ignition gas flows countercurrently to the liquid nitrogen 2 in the heat exchanger 4 to cool the liquid nitrogen and return.

The liquid nitrogen of 8 atm is taken out of the phase separation tank 10 and is reduced to 3.1 atm as it passes through the second copper enthalpy expansion throttle valve 12. At this pressure, another gaseous nitrogen ignites in the liquid passing through the valve 12, and the liquid nitrogen remains at 3.1 atm. The fire gas is separated from the liquid nitrogen in the second phase separation tank 14. This ignition gas passes in cocurrent flow with the 8 atmosphere ignition gas produced in the first expansion step and back flows with the liquid nitrogen to return to the heat exchanger 4, whereby the liquid nitrogen is cooled. Part of the liquid nitrogen collected in the second phase separation tank 14 passes through the third expansion throttle valve 16 to be decompressed to 1.3 atm. At this pressure, another gaseous nitrogen ignites in the liquid nitrogen passing through the valve 16, leaving 1.3 atmospheres of liquid nitrogen. The ignition gas is separated from the liquid nitrogen in the third phase separation tank 18. The ignited gas passes in cocurrent with the 8 atm ignition gas of the first expansion step and 3.1 atm ignition gas of the second expansion step and backflow with the liquid nitrogen to return to the heat exchanger 4, thereby cooling the liquid nitrogen. . The residual body nitrogen from the second phase separation tank 14 is further cooled through the heat exchange coil 22 installed in the third phase separation tank 16, and the upper portion of the storage tank (not shown) is also sent. Vapor generated by the boiling of liquid nitrogen of the third phase separation tank 18 passes back to the final liquid nitrogen together with the ignition gas and returns to the heat exchanger.

Line AB is an isostatic curve in FIG. 2 along which the nitrogen is cooled in the nitrogen liquefaction plant. Point B represents the temperature (110 ° K) of the point where liquid nitrogen leaves heat exchanger 36 (FIG. 3). Line DEF defines a "zone" in which the "biphase" state of liquid and gas exists. Lines BGHI, JKL and MNO are copper enthalpy lines. Lines PQ, RS and TU are isobars for gaseous nitrogen.

Considering the first copper enthalpy expansion through the valve 6 in FIG. 1, nitrogen follows the copper enthalpy line BGHI until it reaches point H in the area DEF. Nitrogen is present in the biphase of liquid and gas. In the phase separation tank 10, liquid and gas are separated and the liquid nitrogen is obtained at point J (ignition gas at point P). The second copper enthalpy expansion follows the isoenthalpy line JKL until the nitrogen reaches point K. The second phase separation forms a liquid (ignition gas at point R) at point M. Tertiary enthalpy expansion causes nitrogen to follow the line MNO until point N is reached. The third phase separation produces a liquid at point V (ignition gas at point T). The liquid in the third phase separation tank is evaporated by the liquid in the second phase separation tank and then the liquid is undercooled. The supercooled liquid is sent to a reservoir having a pressure equal to point M and also a temperature between points M and V. Assume that the liquid at point V is obtained after only one dynamic enthalpy expansion. This will include nitrogen along path BGHI until point W is reached. The overall entropy increase in this process is greater than the sum of the entropy increases involved in following the processes GH, JK and MN. This is because the process HI is less steep, while the line segments GH, JK and MN are all steeper (negative slope in each enthalpy graph decreases with temperature drop). The former (according to the invention) is therefore thermodynamically more efficient than the latter process, since carrying out one dynamic enthalpy expansion results in greater irreversibility than carrying out three successive enthalpy expansions. Moreover, the use of at least three dynamic enthalpy expansions reduces the amount of working fluid in which irreversible work is performed at each dynamic enthalpy expansion after the first one.

It can also be seen that greater efficiency gains can be achieved if point V is reached through 4 or 5 or more continuous enthalpy expansions. In practice, however, more than five dynamic enthalpy expansions reduce other benefits, making the feasibility of the swelling slim.

It can also be seen that the first copper enthalpy expansion (BGH) is less efficient than the second and third copper enthalpy expansions, since the BG process involves a relatively large entropy increase. At temperatures below the temperature of point H, the isobar AB converges to the region DEF. Therefore, it is conceivable that it is more advantageous to isothermally cool until the temperature falls to point J and to carry out enthalpy expansion of up to three times from here. However, this practice is not beneficial because it results in the loss of excessive thermodynamic efficiency in the thermal expansion of the working fluid required to cool the nitrogen to the point where the dynamic enthalpy expansion takes place, and furthermore, the increase in entropy between J: J follows the copper enthalpy line. Greater than BG

Referring back to FIG. 1, there are various methods of producing a stream of nitrogen 2 at a temperature of 113 ° K and a pressure of 45 atm. The plant described in FIG. 3 includes a method of producing such a stream of nitrogen.

In FIG. 3, a heat exchanger 32 of a nitrogen stream 30 at room temperature (300 ° K) and a pressure above the critical pressure (45 atm) is passed through a hot end 34 and a cold end 36. And heat exchangers 38, 40, 42, 44, 46, 48 and 50 are in turn constructed and each heat exchanger is gradually just above (in the flow direction of the main stream 30) It is operated at a lower temperature than the heat exchanger. Stream 32 leaving heat exchanger 50 has a temperature of 110 ° K. It expands through the throttling valve to produce 8 atm liquid nitrogen and 8 atm ignition gas. The ignition gas 58 of the first phase separation tank 56 returns from the cold end 36 of the heat exchanger 32 to the hot end 34 in the countercurrent direction with respect to the stream 30.

The liquid nitrogen from the separation tank 56 is squeezed with copper enthalpy through the throttling valve 60 to produce 3.1 atmospheres of liquid nitrogen and ignition gas. The liquid nitrogen is separated from the ignition gas in the second phase separation tank 62. The ignition gas stream 64 leaves the separation vessel 62 and returns to the hot end 34 of the heat exchanger 32 from the cold end 36 to the hot end 34 while exchanging heat in the countercurrent direction with the nitrogen stream 30. Some of the liquid collected in the separation tank 62 is enthalpy expanded through the throttling valve 66 to produce 1.3 atmospheres of liquid nitrogen and ignition gas. The liquid nitrogen is separated from the ignition gas in the third phase separation tank 68. The ignition gas 70 leaves the third phase separation tank 68 and returns while exchanging heat in the countercurrent direction with the stream 30 from the cold end 36 of the heat exchanger 32 to the hot end 34. The liquid from the separation vessel 62 is further cooled in the coil 72 installed in the third phase separation vessel 68 and then goes to the reservoir. The liquid nitrogen of the third phase separation tank 68 is evaporated by the liquid nitrogen of the second phase separation tank 62 and the vapor generated therein joins the ignition gas 70.

The ignition gas streams 58, 64, and 70 are all sources of cooling of the heat exchanger 32 and are effective in reducing the temperature of the nitrogen stream 30 from 113 ° K to 110 ° K. Typically, ignition gas is produced at 52% when liquid nitrogen passes through the reservoir. The pressure at which the ignition gas is generated is determined by the compressor pressure where it returns from the hot end 34 of the heat exchanger 32.

The stream of nitrogen working fluid 76 in the first working fluid cycle 77 at a pressure of 34.5 atm and a temperature of 300 ° K is continuously subjected to heat exchanger 30 and 40 in cocurrent flow with the nitrogen stream 30. Pass (42) (44) and (46) in turn and leave heat exchanger 46 at a temperature of 138 ° K. This stream is then thermally expanded to a pressure of 16 atmospheres in a "low temperature" expansion turbine 78. The temperature of the working fluid stream 80 leaving the turbine 78 is 112 ° K so that the fluid passes through the heat exchanger 48 in the counterflow direction with respect to the stream 30 to meet the required amount of refrigeration for this heat exchanger. Passes through heat exchangers 46, 44, 42, 40 and 38 in turn.

In the second working fluid cycle 81, a portion of the nitrogen stream 30 is taken at a temperature of 163 ° K between the "cold" end of the heat exchanger 44 and the "hot" end of the heat exchanger 46 and the first intermediate expansion. This stream expands through the turbine 82 and leaves the turbine 82 as a stream 84 at a temperature of 136 ° K and a pressure of 23 atmospheres. Stream 84 is reheated while passing through heat exchanger 46 in the counterflow direction to stream 30 and taken at a temperature of 150 ° K at the heat exchanger intermediate point. This is again thermally expanded through the second intermediate expansion turbine 86. The result is a nitrogen stream 88 at a temperature of 136 ° K and a pressure of 16 atm, leaving the turbine 86 and joining the stream 80 between the cold end of the heat exchanger 46 and the hot end of the heat exchanger 48 to exchange heat. It is possible to meet the amount of freezing required for the instrument 46.

Another portion of the stream 30 in the third working fluid cycle 89 is taken at a temperature of 210 ° K between the cold end of the heat exchanger 42 and the hot water of the heat exchanger 44 and this is the “hot” expansion turbine 90. Enter and thermally expand. The nitrogen stream 92 then leaves the turbine at a pressure of 16 atmospheres and a temperature of 160.5 K. Stream 92 then joins stream 80 between the cold end of heat exchanger 44 and the hot end of exchanger 46. Stream 92 thus meets the amount of freezing required for heat exchanger 42.

Conventional Freon freezers 94, 96, 98 are used to freeze the heat exchangers 38, 40, 42, respectively. In this way the temperature of the nitrogen stream 30 is lowered from the initial 300 ° K to 210 ° K at the cold end of the heat exchanger 42.

The compressor system used in the plant shown in FIG. 3 has not been described for the sake of brevity of FIG. This compressor system, however, comprises a multistage compressor having one stage with a suction pressure of 1 atmosphere and a final stage with a discharge pressure of 34.5 atmospheres. One atmosphere of nitrogen is injected into the first stage inlet with the ignition gas of stream 70. The system leaves the hot end 34 of the heat exchanger 32 and then joins the ignition gases 64 and 58 in sequence at the mall. It also joins the return stream 30 of the working fluid expanded in the increased stage of the compressor. Each of streams 58, 64, 70, and 80 is fed from another stream to the other end of the compressor. Part of the gas leaving the multistage compressor forms stream 76. The remainder is further compressed to 45 atmospheres by four boost compressors operating in each expansion turbine and used to form the nitrogen stream 30. Each stage of the multistage compressor and each boost compressor has its own water cooler installed to remove heat from the compressed gas.

The factory shown in FIG. 3 is represented by application in FIG. Plants suitable for attenuating the nitrogen stream at pressures above 45 atm (eg 50 atm) are similarly represented in FIG. The main difference between the plant of FIG. 5 and the plant of FIG. 4 is that the former uses four single expansion turbines, while the latter uses only two single expansion turbines. Other turbines ("hot" turbines) compress nitrogen at 210 ° K and lower its temperature to 150 ° K, while turbines ("low temperature" turbines) compress nitrogen at 150 ° K to 50 to 14 atmospheres. By lowering the temperature to 110 ° K. Therefore, even if only two monoexpanded streams of working fluid are used to cool the nitrogen product below its critical temperature, the high pressure of this stream makes the temperature-enthalpy prodyl (not shown) of the relief small. Thus, the temperature-enthalpy profile of the stream to be recovered can be kept to be substantially consistent with the temperature-enthalpy profile of the resulting nitrogen stream.

Referring back to FIG. 3, the nitrogen stream 80 is gradually heated because it passes in the direction of the hot end 34 of the heat exchanger 32. Assuming that this passage is actually carried out in an isostatic process, this means that the nitrogen working fluid follows the isostatic process as one of those described in FIG. 6 is a collection of curves showing the change in the specific heat of nitrogen with respect to temperature at various pressures ranging from 1 atmosphere to 25 atmospheres. The left axis end of each isobar is terminated at the saturation temperature of gaseous nitrogen. It can be seen that at any temperature lying on the isobar, the higher the pressure of the isobar, the greater the specific heat of nitrogen and thus the greater the freezing capacity at that temperature. The difference in specific heat at high temperatures at high pressures at any temperature increases with increasing pressure, and this increase is particularly significant above 10 atm.

Claims (9)

In the method of liquefying a permanent gas stream, the permanent gas is nitrogen and the cooling required to reduce the elevated permanent gas stream temperature below the critical temperature and run the two nitrogen working fluid cycles to lower the permanent gas temperature below the critical temperature. Each working fluid cycle performs (1) compressing the working fluid, (2) cooling it, (3) expanding it again, and (4) expanding the working fluid back into the permanent gas stream to exchange heat for permanent It consists of cooling the gas stream and warming itself so that the permanent gas stream is cooled by expansion and cooling of the working fluid, and in one working fluid cycle, the expanded working fluid is at room temperature above the critical temperature. Backflow heat exchange with the permanent gas stream, which is below the critical temperature, inflates this permanent gas stream several times Remove the ignition gases from a liquid, and from, the ignition gas and some liquefied permanent gas stream characterized in that the permanent gas stream and the heat exchanger is made of a phase constant enthalpy expansion than copper step 3 to execute. The liquefaction method of Claim 1 which performs a 3rd, 4th or 5th continuous copper enthalpy expansion operation. The liquefaction method according to claim 1, wherein the ignition gas heat exchanges with the permanent gas stream at a lower permanent gas stream temperature than when the monoexpanded working fluid exchanges heat with the permanent gas. 4. The liquefaction method according to claim 3, wherein the first copper enthalpy expansion operation is performed on a permanent gas having a temperature of 107 to 117 ° K, and the permanent gas is nitrogen. 2. The working fluid cycle of claim 1 wherein the working fluid cycle produces a working fluid above a critical temperature and the working fluid in between the low and high temperature stages expands to medium pressure, reheats, and then expands to a lower pressure. Liquefaction method. 6. The liquefaction method according to claim 5, wherein when the working fluid expands to low pressure, the expanded working fluid can be produced at the same temperature as obtained by the single expansion to medium pressure. The liquefaction method according to claim 1, wherein the permanent gas stream undergoes heat exchange with the permanent gas stream at or above a temperature at which the working fluid expanded into one or more coolant streams is heat exchanged. 8. The liquefaction process of claim 7, wherein the coolant stream cools the permanent gas stream in a room temperature range of 210 ° K or less. The liquefaction method according to claim 1, wherein the multi-stage compressor is compressed to produce a boosted permanent gas, and the ignition gas exits one stage of the compressor and enters another stage.

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